The invention relates to a replica lens having a glass lens body with a refractive surface having a replica skin of a cured synthetic resin. The replica skin is a correction skin having a free surface of the desired, usually very accurate, optical shape. The terms replica lens and replica skin refer to the manufacturing method, namely the replica process or copying process.
In this process a matrix is used which is manufactured, for example, from metal or glass and which has a surface which, apart from a possible shrinkage correction, is the exact negative of the desired refractive surface of the optical component to be manufactured by means of the said process, for example, in particular a lens. A glass lens body which is sometimes termed preform or substrate is provided on the refractive surface, for example, a spherical surface, with a small quantity of a liquid, curable synthetic resin composition, For example, a drop of a light-curable or heat-curable synthetic resin composition (lacquer) is provided on the refractive surface. The lens body comprising the drop of lacquer is pressed against the matrix surface, the lacquer spreading between the matrix and the lens body, so that in the final situation the entire refractive surface of the lens body is covered with the liquid lacquer composition. As an alternative the drop of lacquer may also be provided on the matrix surface. After spreading the liquid synthetic resin composition is cured, for example, by using heat or by exposure to light, via, for example, the transparent lens body. Finally the matrix is removed. The resulting replica lens comprises the glass lens body which at its refractive surface comprises a correction skin (replica skin) of a cured synthetic resin composition the free surface of which has a desired optical shape and is the negative of that of the matrix.
The above-described replica process can be carried out in a simple manner. An important advantage of this process is that a glass lens body can be used which has a comparatively simple shape and/or which has been manufactured in a simple manner. An example hereof is a glass lens body which has been manufactured by a simple pressing process and whose refractive surface, for example, a spherical or non-spherical surface, has not been subjected to any further grinding and/or polishing processes. The lens body manufactured by a pressing process will as a rule not have an optically perfect refractive surface. In this surface deviations from shape and unevennesses, for example pits, may be present. The replica skin gives the refractive surface of the lens body the ultimate optically accurate shape.
Applicants have established that a lens manufactured according to the replica process still has non-acceptable inaccuracies in the refractive surface. The deviations in shape and unevennesses in the refractive surface of the lens body will not be fully corrected or smoothed by the liquid resin composition used, because the synthetic resin composition shrinks upon curing.
As a result of this, undesired and unintentional unevennesses will occur in the free surface of the layer of the cured synthetic resin composition. The deviations in shape and unevennesses in the refractive surface of the lens body itself are as it were transmitted in a weakened form to the free (optical) surface of the cured lacquer layer. This latter surface is the important, refractive surface of the replica lens.
In order to avoid these problems mentioned by the Applicants the primary cause might be removed and it would hence have to be ensured that no irregularities, for example unevennesses, occur in the refractive surface, for example, the spherical surface, of the glass lens body. However, this means a very careful grinding and polishing process so that series production is not readily possible or will otherwise lead to very expensive products.